The invention relates generally to outboard engines, and more particularly, to the oil injection systems for two-stroke internal combustion engines.
Known v-type internal combustion engines for marine use include a cylinder block having a crankcase and two banks of cylinders extend radially from the crankcase. In a six cylinder engine, for example, each cylinder bank includes three cylinders. Each cylinder includes a sleeve and a piston moves relative to the sleeve between top dead center and bottom dead center positions. A main exhaust passageway and cooling water passageway are located between the first and second cylinder banks.
In operation, the friction between the pistons and the sleeves can result in generation of heat and wear of both the pistons and the sleeves. To reduce such heat generation and wear, oil should be dispersed between the pistons and the sleeves. The clearance between the pistons and the sleeves, however, is only about 0.004 to 0.010 inches. Dispersing oil between the pistons and the sleeves is difficult due to such small clearance.
Known attempts to introduce oil directly into the clearance space between the sleeves and the pistons have not been successful. Specifically, the oil supply hole for each cylinder must be located at the outer side of each cylinder due to the location of the exhaust and water passageways. Therefore, the oil supply holes for both banks of cylinders must be located in the outer cylinder walls.
In a v-type engine, and as the crankshaft rotates in a clockwise direction, the pistons in the first cylinder bank are thrust against the inner cylinder walls, and the pistons in the second cylinder bank are thrust against the outer cylinder walls. The second cylinder bank pistons thrust against the outer cylinder walls, and therefore against the oil supply holes in the outer cylinder walls, inhibit oil from being introduced into the cylinder through such holes. As a result, the second cylinder bank may be starved for lubrication.
It would be desirable to provide an oil injection system which injects oil directly between the pistons and the cylinder sleeves in a v-type engine. It also would be desirable to provide such a system which does not add significant costs or complexity to fabrication and assembly of the engine.
These and other objects may be attained by oil injection apparatus and methods for injecting oil directly between the cylinder sleeves and the pistons of both cylinder banks in a v-type engine. In one embodiment, an oil port in the engine block extends to an annular groove in the cylinder wall. An oil pump supplies lubricating oil to the port via a conduit and under the control of a control unit.
In operation, if the piston is thrust into the cylinder wall at the location of the groove when the oil is being injected, the oil flows into the groove and is dispersed as the piston moves past the groove on the next stroke. If the piston is not thrust into the cylinder wall at the time oil is introduced, the oil flows into the cylinder and is dispersed by the piston.
Such direct injection of the oil at a location between the piston and the cylinder wall provides the advantage that lubricating oil is located between the piston and the cylinder in each cylinder. As a result, there is less friction between the pistons and the cylinders as compared to the friction if no lubricant is provided between the pistons and cylinders. Therefore, less heat is generated (i.e., less energy loss) due to such friction, and wear of the pistons and cylinders is reduced.